Xerographic copying apparatus



Jan. 3l, 1967 c. R. MAYO XEROGRAPHIC COPYING APPARATUS Original Filed Dec. 21, 1955 2 Sheets-Sheet 1 FIGI FIG. 2

Flos

FIG.4

:ogoaooafe NEGATIVE POLARI TY SOURCE HIGH VOLTAGE FIG INV ENTOR.

CL VDE R. MAYO Jan. 31, 1967 c. R. MAYO 3,301,152

XEROGRAPHIC COPYING APPARATUS original Filed Deo.' 21, 195s 2 Sheetsshee 2 HIGH VOLTAGE SOURCE F'IG INVENTOR. cL V05 R. MA Yo A T TORNE Y n'United States Patent XERGGRAPHC CGPYNG APPARATUS ClydeR. Mayo, Rochester, N.Y., assignor to Xerox Cor- V poration, Rochester, NXY., a corporation of New York Continuation of application Ser. No. 181,414, Mar. 21, 1962, which is a division of application Ser. No. 318,104, June 4, 1,959, which-in furnis a division of application Ser. No. 399,293, Dec. 21, 1953, now Patent .'No. 2,895,847, dated July 21, 1959. This application Nov. 27, 1964, Ser. No. 416,195 a Y -7 Claims. (Cl. 95-1v.7)

This application is a continuation of my copending application Serial No. 181,414 filed MarchV 21, 1962, now abandoned which in lturn is a division of my parent case Serial No. 818,104 tiled Iune 4, 1959, now abandoned, which in turn is a division of Serial No. 399,293 iiled December 21, 1953, now Patent No. 2,895,847. This invention relates in general to a method and apparatus for development of an electrostatic image, and in particulartrelates to an improved method and apparatus for the deposition of visible powder material on an electrostatic image in conformity with an image such as, for example, the development of a xerographic image or the like.

In xerography, it is usual to form an electrostatic image corresponding to a pattern of light and shadow to be recorded, and to develop this image or make it visible by deposition of electroscopic material thereon. Most simply and directly, a photoconductive insulating layer is electrically charged and exposed to a light pattern whereupon the charge is selectively dissipated to yield an electrostatic charge pattern on its surface, this charge pattern generally being called anlelec-trostatic latent image. In order toutilize this latent image in the production of a visible print, it ultimately is desi-red to deposit visible material in conformity with the image. One method of accomplishing this result is disclosed in Wise Patent 2,618,- 552 in which la two-component developer mixture is cascaded or rolled across -an image-bearing surface to deposit powder particles in conformity with the image, while other systems such as those disclosed in Carlson U.S. 2,297,691 Iemploy sprayed dust particles or other means or methods for deposition on the electrostatic latent image. These various systems of development have their relative merits and disadvantages. For example, the cascading system is quick and-easy and is well adapted to the formation of dense black images of high contrast. However,it gives rise to problems in maintenance of proper relative proportions ofthe two components during prolonged operation and gives rise to many mechanical problems in feeding the two-component developer to the imagebearing surface.

' Now, in accordance with the present invention, there are 'provided means, methods, and mechanisms for the devel-opment of an electrostatic latent image whereby powder particles or the like are carried to an imagebearing surface by a support layer such as a web, sheet or the like and are deposited thereon in conformity with said image to yield a print of excellent quality. The invention is particularly vwell suited to xerography in that it is inexpensive, convenient, and well adapted to automatic operation.

The general nature of the present invention having been set forth, there will now be presented a more detailed description in illustration but not limitation on the invention in the following specification and drawings in which: "FIG. 1 is a diagrammatic side cross section of an insulating surface supporting an electrostatic latent image;

FIG. 2 is a diagrammatic side cross section of developing" mechanism for developing the image illustrated in FIG. 1',

lareas on an insulating surface.

FIG. 3 is a diagrammatic side cross section of an imagebearing member and development member immediately after development has taken place;

FIG. 4 is a diagrammatic side cross section of a development member according to one embodiment of the 1nvention;

FIG. 5 is a diagrammatic view of development mechanisdm `according to another embodiment of the invention; an

FIG. 6 is adiagrammatic view of an automatic xerographic machine according to the present invention.

The present invention is .particularly intended and adapted for the development of an electrostatic latent image, such as particularly a latent image of relatively fine. detail composed of relatively charged and uncharge Such an image may, for example, be an electrostatic latent image corresponding to a pictorial subject such as a conventional photograph, snapshot, or the like, or may be an electrostatic latent image corresponding to a document, manuscript, or other representation of information to be reproduced. Images of this sort, and other images requiring an optical resolution in the order of about ten lines per millimeter or better, form the usual subject of development according to conventional Xerographic systems.

Illustrated in FIG. 1 is such an image system, presented diagrammatically, comprising a xerographic member generally designated 10 consisting of a conductive backing member 11 and an insulating layer 12 thereover, which insulating layer desirably may be a photoconductive insulator. On or near the surface of the insulating layer 12 is an electrostatic image designated by the plus marks 14 at the surface of this layer. It is to be understood that the electrostatic latent image may be of either positive or negative polarity and may consist of gradations of potential or char-ge or may be, as illustrated in the ligure, areas of charge interspaced by areas of substantially no charge. The particular image illustrated in FIG. 1 may be regarded as a line copy image consisting of respective areas of charge and absence of charge which desirably can be printed as areas of black on a white background.

In FIG. 2 is shown, diagrammatically, developing means and apparatus suitable for developing the image illustrated in' FIG. 1. Thus, for example, there is shown an insulating layer 12 having electrostatic image areas 14 on one surface thereof. For this reason, disposed over that insulating layer is la development member being a sheet or web generally designated 15 consisting of a sheet or web of a support material 16 such as a sheet of paper, plastic, cloth, metal such as ialuminum foil, metal-backed paper, or the like, on one surface of which is a loosely adhering coating of electroscopic material 17 consisting of finely divided powder particles electrostatically Iadhering to the surface of the support member 16. These powder particles may be any suitable xerograp-hic toner material, this being generally a finely divided powder material which is visible against a printing surace, such as a surface of paper or the like, and Iwhich is electrostatically Iattractable to kan electrostatic latent image. It may, for example, consist of finely divided pigment particles or finely divided compositions of colored or pigmented resins or the like such as are well known to the art of xerography. Positioned `and disposed -at the reverse side of the development member or web 15 is a contact member such 4as a roller 18 or the like adapted to bring the development member uniformly against the image-bearing surface. This contact member serves to achieve substantial contact between the development member 15 and the image surface, and it is presently believed that pressure is unnecessary except to the extent needed to assure good contact. Desirably, the contact roller 3 or like may be movable across the surface so as to bring the development web or sheet into contact at all pore' tions of the image-bearing surface and thus, for example, the roller 18 is rotatively mounted on a handle 19 and is adapted t-o -be rolled across the entire surface.

FIG. 3 is a diagrammatic illustration of a mechanism of the development process illustrating the image-bearing surface 12 and the development member 15 after development of the electrostatic image has been accomplished. It is observed at this stage that a portion of the powder particles 17 originally residing on the development member `15 has been transferred to form an ima-ge body 20 on the image-bearing surface. In general, the powder particles may be regarded as being oppositely charged with respect to the polarity of charge on the image-bearing surface so that these powder particles are loosely secured to the image bearing member by means of the electrostatic attraction between these particles lwhich may, for example, be negatively charged and the electrostatic latent image which in this same example would be positively charged.

FIG. 4 illustrates a specific embodiment of a development member according to the present invention wherein the development member, generally designated 15, comprises a support sheet or web 211 having coated or impregnated thereon 'a coating or layer 22 with a toner composition 17 loosely adher-ing to the coating 212. According to this figure, the support member 21 may be a sheet or 'web of paper, cellophane, or other sheet or web-like material including plastic parts, self-supporting resin films and the like, and is adapted to be a structural support for the development member 'and preferably a structural support which is repeatedly flexible. Impregnated or coated on the surface of the structural support is a suit-able resin film to form a toner support body on at least one surface.

The coat-ing 22 on the support member 21 may be `any of a number of coating or impregnating compositions carefully selected with reference to the nature of the toner particles in the powder layer 17. With any particular-powder composition selected for the powder layer, and lfor a particular type of electrostatic image to be developed, a specific and particular coating or impregnating composition should be chosen in order to give superior results. Thus, for example, there may be selected a developer composition such as is disclosed in U.S. Patent 2,659,670 and in conjunction therewith there may be used as a coating composition a resin material such .as is disclosed in U.S. Patent 2,618,551 as Ia coating composition for a carrier bead or the like. A coating composition of the type selected will be applied to the support sheet or web by coating, impregnating or like methods. In general, better results are achieved with such coated sheets and good development has been re-corded with coated metal foil, paper of both clay-coated and non-coated bases having the carrier coating thereon, cloth such las nylon and the like with the carrier coating, and other sheet-like members as shown in the gure.

Various coating compositi-ons maybe used depending on whether positive or negative polarity images are being developed and depending on the toner or powder employed. For example, in U.S. Patent 2,659,670 there is disclosed a toner comprising a pigmented, modified phenolformaldehyde resin, which toner is commercially available under the name Xerox toner. Used in conjunction with this material such coating compounds as polyvinyl resins, acrylic and methacrylic resins, cellulosic derivatives, and protein materials will, in general, form a coating to impart negative charge to the toner upon triboelectric contact. On the -other hand, asphaltum powder in combination with coatings such as polystyrene will tend to provide' positively charged powder particles.

The layer of powder material 17 on the development member 15 is characterized by being loosely adhering and by being secu-red -to the support sheet or web substantially exclusively by electrostatic attraction. In general, this layer of powder is applied to the suppo-rt member prior to its use as in development by application of .the powder to the support member with mild frictional action. For example, a suitable support sheet of uncoated or coated paper, plastic or the like is treated with a powder composition by brushing the powder onto the surface of the support member with a camels-hair brush or the like. Thus, the' powder layer is readily applied to the paper or like surface. Alterna-tively, a layer of powder may be shaken across or onto the surface of the supportmember or may be applied from a rotating brush bearing a quantity of the toner composition, or by passing the support member into or through a body of such toner composition. In the case of a porous support such as a s-heet of paper, a highly desirable method for applying the powder to the surface is by blowing through the pores of the member a stream of air carrying a suspension of the toner composition. Other methods of depositing t-he powder laye-r on a support member will be obvious to those -skilled in the art. For example, a powder layer formed on a sheet or web in any desired way may be charged by corona discharge or other ion deposition. Likewise, a two-component Xerographic developer as described in U.S. 2,638,416 may be cascaded across a sheet for web, preferably with excess powder or toner, to form a dense deposit of charged powder thereon.

It is to be understood that either positively charged or negatively charged powder may be coated on the development member. Desirably, the surface of the member then should be of opposite t-riboelectric relationship to the powder. Thus, for positively charged powder, the development member surface should be negative with respect to the powder, and where the. layer is coated by cascading, as just described, the granular carrier of the two-componen-tsystcm likewise shouldbe negative with respect to the powder.

In FIG. 5 is illustrated another appara-tus and mechanism for development according tothe present invention. According` to this embodiment, anfelectrostatic latent image on image support 12 is developed by means of a Idevelopment member 15 comprising a support sheet or web 16 and y:a powder layer 17 with a corona discharge electrode 25 connected` to a negative polarity high voltage source 26 and adapted to be passed across the reverse surface of the development member- 15. The development sheet is placed with the powder side against the image-bearing surface 12 and corona electrode 25 is passed across the surface, causing corona discharge from the electrode to charge the development member 15 and secure it rmly `againstthe image-bearing member 12. When-the development member Vis stripped from the image surface, it is found that -asubstantial portion ofthe powder has been transferred to the image surface in the image areas thereof. y p

In FIG. 6 is illustrated a continuous machine adapted to form a xerographic print on a -sheet or web member following upon exposure `to a suitable light source or other source of -a pattern of light. and shadow to be recorded. A cylindrical support 41 is mounted on an axle 42 with drive means comprising a belt 43 operating on pulley 44 from a drive motor or the like 45. The surface of cylinder 41 is coated with an insulating imagebearing surface comparable to surface 12 of FIG. 1 or one or more of such image-bearing surfaces are mounted on a cylinder support. In the embodiment specica-lly illustrated in the ligure, it is to be understood that the apparatus is designed to reproduce from a pattern of light and shadow in wh-ich case the image-bearing surface corresponding to surface 12 of FIG. 1 is a photoconductive insulating surface adapted to receive and retain an electrostatic charge Iand to dissipate this charge upon exposure to light.

Positioned adjacent Yto the path of motion` of `the surface of the cylinder 41 is a charging station 47 comprising, for example, a positive polarity corona discharge electrode consisting of fine wires suitably connected to a high voltage source 48 of potential high enough to cause a corona discharge surrounding the wires. Subsequent to the charging station 47 in the direction of rotation of the cylinder is an exposure station 49 generally comprising sui-table means for imposing a pattern of light and shadow on the surface of the cylinder and including, for example, a projection lens 50 or other exposure mechanism as is conventional inlthe art, preferably operating with slit projection methods to focus a moving image at an exposure slit 51.` Y

Next subsequent lto the exposure station is a developing station generally designated 52 as will be further described hereinafter. Beyond the development station 52 is a suitable transfer station 53 adapted to transfer a xerographic image from the surface of the cylinder to a transfer web 54 which passes from a feed roll 55 into contact with the cylinder surface at a point beneath a transfer electrode 56 and desirably subsequently through a fusing or fixing device 57 to a take-up roll 58. Desirably, elect-rode 56 is'a corona-discharge electrode operably connected to a high voltage source 59 of like polarity with respect to high voltage source 48 whereby an image body deposited on the cylinder surface is transferred to the transfer web. Fusing device 57 permanently fixes a transfe-rred image on the web to yield a completed xerographic print.

Optionally,- a cleaning station 62 may be disposed adjacent to the surface `of cylinder 41 along with other auxiliary devices ortstations or the like, whereby residual powder image, electrostatic charge or other material or phenomenon may be cleaned or erased from the cylinder surface. Thus, for example, a rotating brush 63 driven by motor 64 through belt65 may be brought to bear against the surface of the cylinder to erase residual powder image therefrom, or further charging means, floodlight means or the like may affect electrical or photon controlled operations. f

At the development station, as illustrated in FG. 6, is a development belt '15 passing Iaround roller 67 which is disposed and positioned to bring the belt 15 to firm con tact with thev surface of cylinder 41. The belt 67 also passes around a drive roller 68 and a guide roller 69. Desirably,` drive roller 68 is driven by a motor or other drive means 70 operating through belt 71, preferably to drive the bel-t in the same direction as the surf-ace rotation of cylinder but -at a speed'substantially in excess o-f the speed of rotation of such cylinder. Thus, there is maintained between belt 15 and cylinder 421 a sliding contact which serves the dual purpose of insuring extremely quick contact between all points of the surface of cylinder 41 and the development belt, and further bringing to each point of the cylinder surface a substantially greater quantity of the powder layer than is carrie-d by any one point of the developer belt.

lAdjacent to one portion of the path of motion of the developer belt 15 is a powder-loading station which may, for example, comprise a developer hopper 74 containing a supply of developing powder, preferably as mixed powder and carrier developer.` This hopper opens against the-development web or belt 15, `whereby the belt lpasses in contact with the developer supply and is coated with powder as the belt passes upwardly `against the developer. Other belt loading mechanisms may, of course, be substituted for-the one shown herein.

In operation of the invention in general, a xerographic electrostatic latent image or like electrostatic latent image is formed on an image-bearing surface 12 and the develsurface 1.2 is obtained, for example, by means of rolle-r 18V of FIG. 2 or roller 67 of FIG. 6, or other like device `-or mechanism; After the entire surface -of the developrnent-member'has been 'broughtinto contact with the electrostatic latent image-bearing surface, the development member is removed from the surface leaving an image body deposited thereon. This image body is utilized as may be desired, and in FIG. 6 is illustrated the ultiza'- tion of this image body iby transfer toa transfer web followed by fusing or permanent fixing of the image body inits configuration thereon. I

The operation of the invention according to the -device of FiG. 6 is generallyI in accord with the operation as applied to all figures. Thus, for example, a xerographic photosensitive member on the surface of cylinder 41 is carried past the charging station wherein an electrostatic charge is applied to the photosensitive member. According to present commercial xerographic operations, this surface charge is of positive polarity. The cylinder then rotates to bring the charged surface to an exposure station where a pattern of light and shadow to be recorded is imposed on the surface of the charged xerographic member, and the charge is thereby selectively dissipated to leave an electrostatic latent image. The image-bearing surface then passes to the development station where it is firmly contacted by development member 15. As the process continues, development member 15 constantly passes through the loading zone wherein additional toner or ypowder is applied to the surface of the support memlber, and this relo-aded surface is continuously again brought into contact with the surface of cylinder 41, The relative speed of motion of belt 15 and cylinder 4&1 may be varied according to t-he individual needs and purposes. Thus, for example, the two surfaces may be in synchronized motion whereby substantially no slippage occurs. However, it has been yfound, surprisingly enough, that sliding motion has certain advantages, chief among which are the increased degree of point contact achieved between various points of the surfaces of the two members and the additional fact that a greater quantity of toner or powder can thus be carried to the image surface. Contrary to expectations, sliding contact seems not to cause smearing of the deposited image body. It is presently believed desirable to adj-ust the relative motion of the members so as to bring a greater area of belt 15 into contact with a lesser area o-f cylinder 41. Thus, it is generally desirable to operate belt 15 and cylinder 41 at different speeds with the .motion generally being in the same direction and with belt 15 traveling at a speed substantially greater than the speed of travel of cylinder 41. Desirably, the belt may travel at a speed slightly in excess of the rate of travel over the cylinder, up to a speed of as much as 5 to l0 times as fast as the travel of the cylinder.

At the transfer station, the image body deposited on the image surface at the development station is transferred to a print support member such as a continuous roll of paper -or the like to yield a xerographic print which desirably is made permanent by heat or vapor yfusing or the like. As illustrated in Schaffert Patent 2,576,047, this transfer may be achieved by a corona discharge electrode of the same Ipolarity as the charging electrode 47. Other methods of transfer to a sticky surface or the like are known to the art and are within the scope of the invention as are other means or methods either obviating transfer or employing transfer mechanism of different types.

Leaving the transfer station member are two members, the trans-fer web 54 bearing the powder image body corresp-onding to the pattern of light and shadow being recorded and .the xerographic photosensitive surface which may bear a residual powder image and/or residual electric char-ge resulting from the previous steps of the operation. The photosensitive surface is prepared again for renewal of the cycle of operations by such cleaning or regeneration steps or techniques as may be desired. A mechanical cleaning operation to remove the residual powder images is specifically disclosed in the figure but it is to be understood that other mechanical or electrical preparation steps may `be employed.

Y adhering to the surface of the paper.

vimage-bearing surface.

'der deposit was substantially completely removed.

Many modifications .may be made without departing from the scope of the invention. Thus, development may be carried out on a sheet or web, preferably a very good insulator, overlying an image-bearing surface .as by passing web 54 of FIG. 6v between cylinder 41 and belt 15 or by similar modications of the other figures. lIn View of these and other modifications, the following examples are in illust-ration, not limitation of the invention.

Example I A xerograp-hic toner pre-pared in accordance with U.S. Patent 2,659,670 andavailable under the name Xerox toner was employed as a developer material for a xerographic image consisting of an electrostatic charge pattern corresponding to typed information. This toner was placed -on the sunface of a -bond paper by casca-ding over the paper a mixture of this toner with a carrier composition as disclosed in Walkup U.S. 2,618,551. Several passes of developer mixture over the pape-r were made until the paper was thoroughly covered with toner and a substantially uniform coating of the toner was loosely The powder-coated paper was placed on the image-bearing surface with the .powder coating face down, and the sheet was pressed into contact with the image surface by means of a rubber roller which was passed lightly kover the back sur- Zfface. The sheet was then removed from the image surface and a deposit of powder in the configuration of the electrostatic image was observed on the image surface. This powder or image body was then transferred to a second sheet of pa-per by conventional methods to yield a xerographic print.

Example II Aand the coated paper sheet was then employed as a developer member as in the previous example. In this case, it was observed that a slightly heavier powder de- Vposit could be -obtained on the surface of the sheet and a substantially denser image body was developed on the The ydeveloper sheet member ikewise was characterized by areas from which the pow- These areas were corresponding to the deposition areas on the image-bearing surface. The developer sheet member, therefore, is a photographically negative copy of the comi pleted xerographic print, which was formed on the imagebearing surface.

y Example III The procedure of Example I was repeated with a sheet of cellophane which was dusted with powder from a camelshair brush to form the developer member. Upon completion of the developing procedure there was formed a developed image body on the image surface and a negative transparency comprising the cellophane sheet and the residual or untransferred powder thereon.

- Example IV The procedure of Example I was repeated employing Aa sheet of bond paper dusted with toner powder. This :sheet was placed face down on a plate bearing a xerographic electrostatic latent image, and w-as held in firm contact therewith by means of a weighted roller. The ldeveloper sheet was removed from the image surface by a sliding action in which the sheet was slid along the surface in one direction while the roller moved down the surface-in an opposite direction, thus causing sliding con- .tact between the developer sheet andthe image surface.

sheet in lines corresponding yto image areas on the plate and a clear image of typed information was represented on the image-bearing surface by developer or toner material removed fro-m the developer member. The image body was transferred to a second sheet of paper to yield a xerog-rap'hic print ofv substantially increased density with respect to the print of Example I; Resolution in the deposited image was about 15 lines per millimeter, and did not show substantial directional difference.

What is claimed is:

1. Apparatus for developing an electrostatic ylatent image comprising a conductive cylinder having a photoconductive insulating layer on its curved surface and rotatably 4mounted on its longitudinal axis, drive means to rotate said cylinder and, sequentially mounted around the periphery of said cylinder in the direction of rotation, a .high voltage char-ging means, an optical exposure station, a developing station, a transfer station anda cleaning station, said developing station comprising ya support web positioned wit-h one surface adapted to be brought into firm contact with the curved cylindrical surface, means to press one portion of said support web into 'con-4 tact wit-h said c-u-rved cylindrical surface, drive means adapted to -move said support web non-synchronously relative to said cylinder but in the same direction as the direction 'of peripheral movement of said cylinder at the point of contact between said web and said cylinder, so that said web moves relative to said cylinder and means removed from the cylindrical surface for applying to the web surface a relatively uniform coating of finely-divided powdered material charged to an electrostatic potential sufficient to cause adherence of said powder to the web surface and to cause selective adherence of said powder' to said cylindrical surface in conformity with electrostatic charges thereon.

2. A xerographic apparatus comprising:

(a) a xerographic drum, 1 l

(b) means to form a latent electrostatic image on said drum, and

(c) means to develop `a latent electrostatic image `formed on said drum by moving an electroscopic pigmented :powder-laden web in sliding contact against the Asurface of said drum with said powder against said drum. l

3. An image developing apparatus comprisingmeans to support a member having a surface bearing a latent electrostatic image thereon and an image developing station, said developing station including:

(a) a donor member transparent to visible light;

(b) means for applying to said donor member a uniform coating of finely-divided electroscopic developing powder; and,

(c) means for bringing the powder coated side of said donor member intocontac't'with said latent imagebearing surface and then separating the two, w-h'ereby a developed image is formed on said-surface and a yreverse transparency of said image is formed on said transparent member.

4. An image developing apparatus comp-rising means to support a member having a surface bearing a latent electrostatic image thereon and an image developingstation, said -developing station includingi l (a) a donor member transparent to visible' light;

(b) means for applying to said donor member a uniform coating of finely-divided electroscopic'developf ing powder; yand,

(c) means for bringing the powder coated side of said donor member into contact with said latent imagebearing surface and then separating the two, the

-thickness yof said coating of .finely-dividedv powdered material being'selected so that it is substantially completely removed in areas of said W'eb'whioh contact the most highly charged areas of said cylindrical surface during development, whereby a clean background reversal image of the image on said surface is left on said web after develop-ment.

5. Apparatus Ifor developing a latent electrostatic image comprising:

(a) Imeans to support a member having a surface bearing `a latent electrostatic image thereon;

(b) a donor member;

(c) means for applying a uniform coating of nelydivided electrosc-opic developing powder to a surface of said donor member;

(d) means for bringing the powder coated surface of said donor member into contact with said latent electrostatic image-bearing surface and sliding said donor member with respect thereto; and,

(e) means to remove said powfder coated donor member from contact with said latent electrostatic ima-ge bearing sur-face whereby a visible image is produced on said latent electrostatic image-bearing surface by virtue of particle transfer thereto.

6. An `apparatus according to claim 5 including means to l:move said latent electrostatic image-bearing surface and means to move said powder coated donor web in slid- 10 ing contact therewith at a speed between slightly in eX- cess of and about l0 times the speed of said latent electfostatic image-bearing surface.

7. An apparatus according to claim 5 in which `at least the surface of said donor member which is to be coated wit-h electroscopic developing powder has .a triboelectric relationship opposite to said powder whereby powder deposited thereon tends to adhere thereto and prevent the deposition of electroscopic powder ofn said latent electrostatic image-bearing surface in background areas during development.

References Cited by the Examiner UNITED STATES PATENTS 2,703,280 3/1955 Butterfield et al. 95-1.7 2,811,465 10/1957 Greig 95-1.7 X 2,829,025 4/ 1958 Clements et al. 346-74 2,895,847 7/1959 Mayo 95-1.7

JOHN M. HORAN, Primary Examiner. 

1. APPARATUS FOR DEVELOPING AN ELECTROSTATIC LATENT IMAGE COMPRISING A CONDUCTIVE CYLINDER HAVING A PHOTOCONDUCTIVE INSULATING LAYER ON ITS CURVED SURFACE AND ROTATABLY MOUNTED ON ITS LONGITUDINAL AXIS, DRIVE MEANS TO ROTATE SAID CYLINDER AND, SEQUENTIALLY MOUNTED AROUND THE PERIPHERY OF SAID CYLINDER IN THE DIRECTION OF ROTATION, A HIGH VOLTAGE CHARGING MEANS, AN OPTICAL EXPOSURE STATION, A DEVELOPING STATION, A TRANSFER STATION AND A CLEANING STATION, SAID DEVELOPING STATION COMPRISING A SUPPORT WEB POSITIONED WITH ONE SURFACE ADAPTED TO BE BROUGHT INTO FIRM CONTACT WITH THE CURVED CYLINDRICAL SURFACE, MEANS TO PRESS ONE PORTION OF SAID SUPPORT WEB INTO CONTACT WITH SAID CURVED CYLINDRICAL SURFACE, DRIVE MEANS ADAPTED TO MOVE SAID SUPPORT WEB NON-SYNCHRONOUSLY RELATIVE TO SAID CYLINDER BUT IN THE SAME DIRECTION AS THE DIRECTION OF PERIPHERAL MOVEMENT OF SAID CYLINDER AT THE POINT OF CONTACT BETWEEN SAID WEB AND SAID CYLINDER, SO THAT SAID WEB MOVES RELATIVE TO SAID CYLINDER AND MEANS REMOVED FROM THE CYLINDRICAL SURFACE FOR APPLYING TO THE WEB SURFACE A RELATIVELY UNIFORM COATING OF FINELY-DIVIDED POWDERED MATERIAL CHARGED TO AN ELECTROSTATIC POTENTIAL SUFFICIENT TO CAUSE ADHERENCE OF SAID POWDER TO THE WEB SURFACE AND TO CAUSE SELECTIVE ADHERENCE OF SAID POWDER TO SAID CYLINDRICAL SURFACE IN CONFORMITY WITH ELECTROSTATIC CHARGES THEREON. 